The worm's file is a PE executable 9343 bytes long packed with a modified UPX file compressor. The unpacked file's size is about 19 kilobytes.
When the worm's file is run, it first deletes the FTPUPD.EXE file. Then the worm creates a mutex with the "uterm13" name. This is done to avoid loading multiple copies of the worm into memory.
Next, the worm deletes Registry key values and terminates processes with any of the following names:
- Windows Security Manager
- Disk Defragmenter
- System Restore Service
- Bot Loader
- Windows Update Service
- avserve2.exeUpdate Service
- MS Config v13
The key values are deleted from the following Registry key:
After that the worm installs itself to system and creates a startup key for its file in the Registry. The worm's file is copied to Windows System folder with a randomly generated name. The following Registry key is then created:
- [HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run] "Windows Update" = "%WinSysDir%\<random>.exe"
where WinSysDir represents Windows System directory name and <random> represents random characters. The name of the worm's file can be for example 'sjsudf.exe'.
Additionally the worm can create the following Registry key values:
- [HKLM\Software\Microsoft\Wireless] "ID" "Client"
The worm tries to start its spreading routine as a remote thread of Windows Explorer. If this fails, the worm starts the spreading thread directly.
Unlike its previous variants, the worm does not connect to IRC, does not create an IDENT server on port 113 and does not start a backdoor on port 3067. Instead, the worm periodically connects to several websites (sometimes, depending on an internal flag, with a specially constructed URL) and reads a file from there. If the file's data does not contain 'zer0' string, the worm waits and re-connects again. But if the file contains 'zer0' string, the worm downloads an executable file from that website to Windows System folder and runs it. It should be noted that the worm performs a secure authentication before the file is downloaded.
Here's the list of websites that the worm tries to connect to:
Additionally the worm can listen on a random TCP port.
The worm spreads to remote computers using LSASS vulnerability. It contacts remote computers on TCP port 445, exploits the vulnerability and copies its file to a remote system.